Various methods may be employed to generate electrical energy, and these methods typically require a high pressure coal supply system. In particular, many of these high pressure systems include high pressure reactors which combust the coal to produce heat or to further refine the carbon from the coal. The high pressure is used to nearly instantaneously combust the coal to produce the desired energy release. Coal, even when highly pulverized, is substantially a solid material and difficult to pressurize to the high pressures needed for combustion. To assist in providing the coal and achieving the high pressures required for combustion thereof, the coal is often formed into a water slurry. The slurry then can be more easily pumped and pressurized to the required high pressures. Generally, it is desired to have the coal pressurized to at least 1000 psi.
Various systems have been developed to provide the high pressure coal required, but these systems all have numerous inefficiencies. With such systems, coal is generally first placed into a slurry of some form. The slurry includes an incompressible liquid, such as water, with the coal particles suspended therein. The carrier fluid of the slurry is also provided to the reactor as a large surplus in the slurry, thereby decreasing the efficiency of the reactor.
Still other systems have attempted to provide a feeder system which uses a screw feeder or pump, but has similar disadvantages. In particular, they generally require a plurality of heat exchangers around the feeder itself to provide the proper temperature of the carbon dioxide (CO2) that is fed into the coal in the feeder. These rely upon high velocity inertia and the incompressibility characteristics of CO2 pumped into the feeder to provide a seal to stop the backflow of the material as it goes from the low pressure input to the high pressure output. These systems do not easily overcome the high pressure head against which the coal is pumped. Finally, there are compressible gas systems that use cycling lock hoppers or sliding cylinders and pistons (see, e.g., Conspray Dynamic Sleeve Piston Coal Feeder, Report No. DOE/MC/14603-1562, Technical Information Center, Springfield, Va. 1984) for pumping pulverized solids to high pressure within a compressible medium. Like those which use incompressible fluids (i.e., water and carbon dioxide, CO2), these later pumps are also very complex and costly.
Accordingly, it is desirable to provide a more efficient less complex system to provide a continuous feed of high pressure coal to a gasification system.